Unidirectional webbing material

ABSTRACT

Improved unidirectional webbing material having a low warp to fill weight ratio and comprised of specially coated and spaced generally parallel warp or carrier strands of a synthetic fiber such as fiber glass interwoven with and securely bonded to spaced groupings of glass fiber weft (fill) elements to provide a distortion resistant and rugged fabric useful for the reinforcement of molded plastic articles and the like.

May 6, 1975 United States Patent [191 Lewis et al.

UNIDIRECTIONAL WEBBING MATERIAL inventors: Albert Lewis, Covina; RonaldG.

Krueger, Azusa, both of Calif.

Kaiser Glass Fiber Corporation,

[22] Filed: Jan. 28, 1974 Appl.No.:436,974

Primary Examiner-Stanley N. Gilreath Attorney, Agent, or Firm-Naylor,Neal & Uilkema Related US. Application Data [62] Division of Ser. No.288,793, Sept. 13, 1972 ings of glass fiber weft (fill) elements toprovide a distortion resistant and rugged fabric useful for the reinl56lReferences cued forcement of molded plastic articles and the like.

UNITED STATES PATENTS 2,360,l09 lO/l944 Converse..........i.............138/144 X 1 Claim, ll Drawing Figures o e u a a a n PATENTEDHAY ems .881,522

sum 1 nr 2 PBJENTEDHAY sms $881,522

sum 2 BF 2 UNIDIRECTIONAL WEBBING MATERIAL RELATED APPLICATION This is adivision of application Ser. No. 288,793, filed Sept. 13, I972.

BACKGROUND OF THE INVENTION This invention relates to wovenunidirectional synthetic fiber webbing materials used in thereinforcement of molded plastic articles and the like. Moreparticularly, it is concerned with providing an improved wovenunidirectional and relatively pliant glass fiber webbing material of alow warp weight to fill weight ratio that can be used as a reinforcementin molded plastic articles of both simple and complex shape.

Webbing materials of the type under consideration are generallyexemplified by such U.S. patents as U.S. Pat. Nos. 2,266,761; 2,769,222;2,77l,659 and 2,887,l 32. Traditionally, if a weaver were to preparewoven webbing material, and particularly webbing of fiber glass with alow warp weight to fill weight ratio, the fabric would have high fabricdistortion characteristics and literally fall apart. For this reason,prior art unidirectional webbings of glass fiber usually had a high warpto fill weight ratio as evidenced by US. Pat. No. 2,887,132. When,however, the bulk of the fibers constituted the warp strands, the wovenfabric or tape lacked the pliability required for many applications andhad but limited utility even though glass fiber tapes ordinarily provideexcellent reinforcing materials. On the other hand, woven fabrics ofsynthetic materials having low warp to weft or fill weight ratio areexceptionally pliable and can be readily used for numerous applicationsnot available to fabrics of high warp weight to fill weight ratios,provided the distortion problem can be corrected.

The high distortion characteristics usually attendant with woven fabricsof synthetic materials having a low warp to fill weight ratio is avoidedin the woven fabric or webbing materials of the instant invention byselectively coating the warp strands with an appropriate chemicalcoating of relatively uniform thickness that serves to bond ormechanically lock the various fill or weft strands to the warp strandsafter the fabric is woven so that the finished fabric will be relativelydistortion resistant. Depending upon the particular chemical compositionof the coating, the bonding of the warp strands to the fill strands canbe effected by various methods or techniques, such as by heat, moisture,the use of organic solvents, or contact pressures. Avoidance orminimization of high distortion in a woven unidirectional glass fiberfabric having a low warp to fill weight ratio means that the fabric canadvantageously be used as a reinforcing tape that can be handled bystandard production equipment without falling apart and, at the sametime, be pliable enough to take various shapes and be readily integratedin molded plastic articles of complex and intricate shape.

SUMMARY OF THE INVENTION It is a primary purpose of the instantinvention to provide an improved unidirectional woven textile fabric ortape of synthetic fibers, and in particular glass fibers, having a verylow warp to fill weight ratio. For example, the fabric can be such thatat least 90% or more of the fabric weight is in the fill direction. Thefabric has excellent distortion resistance despite the aforesaid warp tofill weight ratio and is sufficiently pliable so that it can be used invarious kinds of plastic reinforcement applications where complex shapesare involved without falling apart and while being handled by standardproduction equipment. These advantageous results are obtained byappropriately coating the warp strands of glass fiber or other syntheticfiber with a suitable chemical bonding coating, preferably prior toweaving, so that the warp strands can be firmly bonded or mechanicallylocked to the fill strands or groupings of fill strands or elementsafter the fabric is woven.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an overall schematic andperspective view, with parts broken away, of a typical production linefor continuously forming the distortion resistant glass fiber tape orwebbing of the instant invention;

FIG. II is an enlarged fragmentary perspective view with parts brokenaway taken within the bounds of encompassing line [I of FIG. I andshowing a coated warp strand section wherein the strand is ofmonofilament construction;

FIG. [IA is a view similar to FIG. II showing a coated warp strandsection wherein the strand is of multifiber construction;

FIG. III is an enlarged perspective view of a section of webbing takenwithin the limits of circumscribing line III of FIG. I and shows a warpstrand bonded or mechanically locked to one or more filler strands attheir points of intersection;

FIG. IV is a perspective view of a typical production line for seamlessplastic pipe and illustrates the manner of winding the distortionresistant webbing or tape of the present invention about, and as a partof, the wall of a seamless plastic pipe;

FIG. V is an enlarged cross-sectional view taken along line VV of FIG.IV and illustrates certain details of the wall structure of the pipebeing manufactured by the equipment of FIG. IV;

FIG. VI is an enlarged and partly broken away perspective view of alength of pipe as shown in FIG. IV embodying the webbing of the presentinvention;

FIG. VII is an enlarged cross-sectional view taken generally along lineVII-VII of FIG. VI with parts removed and illustrates certain details ofthe interlocked warp and filler strands of the reinforcing webbing;

FIG. VIII is a perspective view of a modified form of webbing;

FIG. IX is an enlarged fragmentary perspective view of the webbing ofFIG. VIII as taken within the circumscribing line IX thereof showing acoated weft or fill element construction wherein the elements are ofmonofilament construction; and

FIG. IXA is a view similar to FIG. IX showing a coated weft or fillelement construction wherein the elements are multi-fiber construction.

DETAILED DESCRIPTION With further reference to the drawings and inparticular FIGS. l-III, the unidirectional distortion resistant andsomewhat retiform woven fabric webbing or tape 10 of the instantinvention is generally made up of synthetic fibers, e.g. glass fibersarranged as singular and widely spaced glass fiber warp strands l4 andbundles or groupings 16 of individual glass fiber weft or fill strandsor elements 17 interlaced and criss-crossed with the warp strands 14.

Prior to the weaving operation, at least certain and preferably all theparallel and spaced warp or carrier strands 14 that run the length ofthe webbing or tape are advantageously surface treated or covered with asuitable coating preferably uniformly applied to the strands 14 alongtheir full length. The coating 15 to be described more fully hereinafteradvantageously acts as a bonding medium for anchoring the individualglass fiber fillers or weft strands 17 to the warf strands 14 in crosswise relationship or at a bias to the warp strands.

In the preferred embodiment of the invention, the bundles 16 areselectively spaced from each other by a suitable gap or distance so thatinterstices or apertures 20 exist between the bonded together warp andweft elements 14 and 17 and the webbing is somewhat open or net-like instructure. This net-like or retiform structure enhances the flexibilityand pliability characteristics of the fabric without adversely affectingthe overall yield and tensile strengths of the webbing for mostapplications.

The individual glass fiber warp strands 14 can be of monofilamentconstruction 21 as shown in FlG. ll, or each be made up of anappropriate number of helically twisted-together singular fiber glassfilament 210, as shown in FIG. HA. The individual strands 17 of thebundles 16 may similarly be of monofilament or twisted strandconstruction.

The bonding coating 15 is substantially uniformly applied to the warpstrands 14 along their entire lengths and should be fully compatiblewith whatever surface coating or sizing is present on the weft or fillerstrands 17. This is important because in a typical end use applicationthe filler strands 17 are treated or coated with a surface treatment orsizing that is designed to provide full compatibility between the fillerstrands and the plastic composite article, (e.g. a pipe or tube in whichthe webbing 10 is incorporated for reinforcement purposes).

Coating 15 can be made of natural or man-made polymers, copolymers,waxes and mixtures thereof. Representative examples include, withoutlimiting the scope of use to those recited, styrene, butadiene,polybutadiene, polyvinylchloride, polyethylene, polypropylene, polyvinylacetate (plasticized), acrylics, polyvinyl pyrrolidene compounds,natural latex, paraffin wax of the hot melt type, casein, carboxycellulose esters and ethers.

In the illustrated system shown in FIG. I the appropriately coated warpstrands are drawn over a guide 22, woven with the fill elements at ashuttle 23, and then heated and pressed together through a set of heatedrollers 24. The desired temperature range during heating is on the orderof 225 375F. or as high as 500F. depending on the specific coatingcompound used. For all practical purposes, 500F. is the usual upperlimit because at this temperature conventional sizings on the fillstrands ordinarily start to decompose. A practical lower limit is aroundl50F. because below this temperature many coatings have a tendency toself-block or adhere to themselves, causing a non-uniform coatingthickness and other problems.

In addition to heat bonding of the warp coating 15 to filler strands 17,this bonding of warp strands can be effected by other methods dependingupon the particular chemical composition of coating 15. For example, itcan be done by moisture, the use of organic solvents,

or contact pressure provided that at the same time such treatment doesnot adversely affect the surface or sizing coating on the fill elementsand possible destroy the compatibility between the fill elements and theplastic composite that the fill material is to reinforce. Because ofthis desired compatibility it is important that the coating on the fillelements not be deleteriously affected by any warp to fill bondingprocess to be used.

Because of the different types of coatings 15 that can be used topractice the instant invention for the purposes of this application theterm blockable" shall be used in the specification and claims todesignate a coating 15, regardless of its particular composition, thatis capable of bonding fill elements 17 to warp strands 14 when it hassolidified. Such a coating when applied to a warp strand can be eitherin the form of a viscous liq uid, a paste, a plastic material or a waxysubstance and upon hardening or finally solidifying mechanically bondsthe warp strands 14 to the filler elements 17 naturally, or under theinfluence of heat or through a chemical cure of the material.

In all of the bonding techniques mentioned, namely: heat, moisture,solvent and contact bonding, pressure rollers which squeeze the fabricwarp and fill elements together are preferably employed. The heat bondtechnique contemplates heating the woven goods to l50500F. with thedesired range being between 225 and 375F, as noted, and then pressingthe warp and fill strands together to effect bonding. In the moistureand solvent bonding techniques, the woven goods are passed through achamber saturated with either moisture or solvent vapors, with the warpand fill strands then being squeezed together through the medium ofsqueeze rolls. The contact bond technique would require only thatsqueeze rolls be used to cause adherence between the warp and fillstrands as the woven fabric is passed between the rolls.

ln the case of moisture bonding, the various chemical compositions thatcan be used for the blockable coating 15 include polymers ofacrylate-type (polyacrylic acid, polymethacrylic acid, etc.); polyacrylamide; casein; polyvinyl alcohols (partially or fully hydrolyzed);dextrin; low molecular weight polyvinyl pyrrolidone; carboxy celluloseesters and ethers; high molecular weight polyethylene glycols; watersoluble or water swellable natural gums.

The degree of moisture sensitivity can be controlled by blending one ormore of the aforementioned ingredients with materials with less moisturesensitivity such as polyvinyl acetate; acrylic esters; styrenehomopolymers and copolymers; polyesters; epoxy resins.

Suitable contact adhesives for contact bonding of warf and fillerstrands include vinyl ethyl ether resins; plasticized polyvinyl acetate;low molecular weight styrene-butadiene latex and even paraffin waxes.

The FIG. 1 system is typical of that used for producing the distortionresistant unidirectional glass fiber tape or webbing of the instantinvention through a heat bonding process. As indicated in FIG. I,appropriately spaced warp strands 14 are continuously payed out fromspools 27 over the guide 22 then directed through the shuttle 23, andthen fed between the heated pressure rolls 24 to a take up reel 28 in amanner well known in the art. As the individual warp strands 14 to whicha heat bondable blockable coating 15 has been previously applied are fedunder appropriate tension from guide 22 to reel 28, the shuttle 23interweaves the groups or bundles 16 of fill elements 17 with the warpstrands 14 to form the net-like webbing. The interweaving mechanism maybe any one of a number of mechanisms well known in the art (e.g. astandard rapier mechanism or a shuttle mechanism) and does not form partof the invention.

As the webbing is advanced through the heated rolls 24 warp and weftstrands 14 and 17 are heated and the blockable surface coating 15 of thewarp strands l4 plasticizes. At the same time the criss-crossed andinterwoven strands l4 and 17 are selectively pressed together withoutbeing crushed until the weft or filler elements l7 become firmlyembedded in the softened coating 15 of warp strands 14 under theapplication of pressure from rolls 24. The embedded configuration may beseen from FIG. "I. As the webbing 10 leaves rolls 24 and the warpcoating 15 cools and solidifies, the warp strands l4 and weft strands l7become interlocked.

The mechanical locking or bonding of the warp and fill strands l4 and 17as aforedescribed is particularly useful in producing distortionresistant glass fiber tape material of a very low warp to fill weightratio and which otherwise would be readily susceptible to distortion andwould literally fall apart. By virtue of this invention, unidirectionalglass fiber tape or fabric wherein the filler strands make up at least90% of the overall weight of the tape can be commercially produced andused for plastic composite reinforcement purposes.

FIG. IV illustrates a production line for incorporating the tape 10 intoa seamless plastic pipe 30. The basic elements of the production linecomprise a pay-out reel device 32, a dip coating station 34 and amandrel station 36. Dip coating station 34 comprises an appropriatelyheated tank 38 for a coating bath 39 along with a series of idlercoating rolls 40 through which glass fiber tape 10 is threaded. The bathmaterial 39 may comprise a suitable thermoplastic or thermosettingmaterial.

As the web 10 moves through rolls 40, it is caused to be immersed inbath 39 and the entire web 10 including both warp strands l0 and fillerstrands 17 becomes uniformly coated on each side with a coating ofplastic fill material. From the bath 34 the partially hardened plasticcomposite, designated 44, comprised of the coating of fill material andthe web 10 is directed towards and helically wound about a mandrel 46 atthe station 36.

In helically winding the successive leading portions of the plasticcomposite 44 about the mandrel 46 adjacent edges of the generallylongitudinally aligned filler strands 17 of adjoining helical portionsof the web are preferably abutted to form a continuous helical joint 48.As the composite 44 is helically wound about rotating mandrel 46, it isprogressively advanced along the mandrel. When the leading edge of theplastic composite 44 reaches the terminal extremity of mandrel 46, thecomposite will have sufficiently polymerized to provide a generallyseamless plastic pipe 30, as shown in FIGS. V and V1, with the opposingedges of the composite 44 making up the scams or joints 48 havinggenerally merged and coalesced together so as to form a smooth outersurface.

In the above pipe product example, it will be noted that the main fillerstrands 17 of the webbing were generally oriented or aligned with thelongitudinal axis of the final pipe produce, i.e.. they were arranged ina direction where they would function most efficiently as areinforcement element without becoming dislodged from the carrier warpstrands 14.

In the above and other product examples, since tape 10 has a relativelylow warp to weft strand weight ratio due to the spaced arrangement ofindividual warp strands which extend lengthwise of the tape 10, it isrelatively pliant and can be readily flexed about and along itslongitudinal axis without distorting the webbing or materially affectingthe mechanical interlock between warp and filler or weft strands.Depending upon the ultimate strength requirements for a given tape 10each bundle 16 will be made up of more or less individual strands 17and/or adjacent bundles or groups 16 will be spaced further apart orcloser together.

One example of a relatively distortion resistant tape 10 used forplastic seamless pipe comprised a tape wherein parallel arranged warpstrands 14 were spaced from each other at about nine-sixteenths inchwhile adjacent bundles 16 of filler strands 17 were spaced from eachother on the order of three-sixteenths inch on centers so as to form aninterstice 20 having the dimensions of about one-half inch one-sixteenthinch. The individual strands 17 of the groups 16 and the warp strands 14in their uncoated state had a diameter on the order of 0.003 to 0.006inch and each such final warp strand 14 was made up of a series ofhelically wound glass fiber filaments wherein each filament had adiameter on the order of 0.0003 to 0.0006 inch. A coating 15 ofapproximately 0.002 to 0.004 inch thickness was substantially uniformlyapplied to the exterior surface of each warp strans 14 along its fulllength. The individual strands 17 were made up of filaments of glassfiber.

It is also to be understood, of course, that the overall width andlength of webbing 10 in any given case will be dependent upon theresults desired as well as upon the limitations of the equipmentinvolved in producing the webbing l0 and incorporating it in a finalarticle of manufacture. Inasmuch as the warp and weft elements 14 and 17respectively of tape 10 are of relatively minute size and relativelylightweight, e.g., on the order of about 1 pound per 3,000 yards ofstrand length, the overall lightweightness of webbing l0 contributes toits pliability and handling in addition to location of the major portionof the glass fibers in the fill or weft portion of the woven fabric.

In another advantageous embodiment of the instant invention the wovenfabric or webbing of the invention can have a slightly modifiedcomposite construction, such as is shown in FIGS. VIII, IX and IXA. Inthis case, the webbing, designated 50, is comprised of the usual warpstrands 14 and bundles or groups 52 of individual glass fiber fillerelements 54. Each filler element 54 is coated with a substantiallyuniform moisture-resistant coating 56 throughout its length and cancomprise a single monofilament core 55 as shown in FIG. IX or a core 55amade up of a number of twisted monofilaments as shown in FIG. IXA. Themoisture resistant coating 56 can be composed of synthetic and/ornatural polymers. Suitable materials including among others,polyacrylates, polyacrylate esters, epoxy resins, polyesters, polyvinylcompositions, polyethylene glycol, poly styrene (homo and copolymers).As particularly suitable moisture resistant coating materials polyestersand epoxy-type resins can be employed with excellent results. Sincewebbing 50 has filler elements 54 provided with moisture resistantcoatings the resultant moisture tively widely spaced, smooth surfacedand parallel synthetic fiber warp strands intersecting glass fiber fillelements arranged in weft bundles that are interlaced with and arrangedcrosswise to said warp strands, the ratio of said warp strands to saidweft fill elements being relatively low, said fill elements being bondedto said warp strands at their areas of intersection, said tape having auniform coating of polymerized plastic fill material on each sidethereof and providing a seamless hard walled pipe having said glassfiber fill elements substantially aligned with the longitudinal axis ofsaid pipe.

1. A plastic seamless pipe comprising a helically wound relativelydistortion resistant unidirectional tape, said tape being comprised of aplurality of relatively widely spaced, smooth surfaced and parallelsynthetic fiber warp strands intersecting glass fiber fill elementsarranged in weft bundles that are interlaced with and arranged crosswiseto said warp strands, the ratio of said warp strands to said weft fillelements being relatively low, said fill elements being bonded to saidwarp strands at their areas of intersection, said tape having a uniformcoating of polymerized plastic fill material on each side thereof andproviding a seamless hard walled pipe having said glass fiber fillelements substantially aligned with the longitudinal axis of said pipe.